BENGHAZI Libya (Reuters) - Islamists militants in Libya have probably kidnapped up to 25 soldiers who are missing in the eastern city of Benghazi and killed five others, an army commander said on Wednesday, as the two sides battled over control of the airport.

Violent anarchy has taken hold in the port city and in the capital Tripoli, causing the central government to lose its grip on power three weeks ago, three years after an uprising ousted Muammar Gaddafi.

Western powers worry Libya will turn into a failed state or head towards another civil war. Tripoli is in the hands of an armed group linked to the western city of Misrata after it expelled a rival group and forced the elected parliament to relocate to a town in the remote east of Libya.

In Benghazi, Islamist fighters have been trying to seize Benghazi’s civilian and military airport in recent weeks by approaching the site from several sides, residents say. The army has tried to stop the advance with artillery fire.

Five soldiers were killed and seven others wounded when Islamist fighters belonging to a group called Majlis al-Shoura attacked an army checkpoint in Benghazi on Tuesday, Fadhil al-Hasi, a special forces commander, told Reuters.

Majlis al-Shoura refers to an alliance of Islamist fighters in Benghazi that includes Ansar al-Sharia, the group Washington said was behind an attack on the U.S. consulate in Benghazi two years ago during which the then American ambassador was killed.

“Twenty-five soldiers are missing,” Hasi said, adding that Islamists had most likely abducted them during recent fighting at checkpoints in Benghazi. He gave no precise dates.

Hasi also said fighting at the Benina area where the airport is located was continuing, with war planes bombing Islamist positions.

The army special forces have allied themselves with troops of former Gaddafi-era general Khalifa Haftar who has declared war on Islamists in Libya.

NATO and Arab countries have been training Libyan soldiers since the toppling of Gaddafi but Libya’s regular forces are often no match for armed groups battle-hardened from the eight-month uprising in 2011.